TURNER, HAENKE AND HUBBARD GLACIERS 103 nimble of distant thunder; and at rare intervals one may see a huge mass of blue or black ice thrust itself up from below the fiord, some distance from the glacier front, as a part of the submerged ice foot is broken off, and then no report is heard, but the wave that follows is far greater than usual. The water waves which follow the discharge of icebergs from the front of Hubbard Glacier are of great magnitude. In September, 1913, for example, the steamship Princess Maquinna was aground on a reef just west of Osier Island with the members of the International Geological Congress who visited Yakutat Bay under the guidance of the junior author. The ship lay over a mile from the glacier, and yet the water wave following the discharge of icebergs from Hubbard Glacier caused the steamer to roll until she took in water on the main deck, as first one side and then the other was tipped far down by the iceberg waves. There are periods when for an hour or two there is very little discharge, and then periods, fully as long, when scarcely a moment elapses without the sound of ice-falls from some part of the glacier front. It is possible that these differences are in some way related to the state of the tide, but we have not determined whether the periods of quiet and activity form part of a regular cycle or are merely irregular intervals due to accumulation of strain and relief from strain or to expansion and contraction under sunlight. While there are periods of relative quiet, they are not periods of absolute repose, and they occupy far less time than the periods of activity. Day and night the ice falls and the reports that pass out through the air are so frequent that it is fair to speak of the glacier as almost ceaselessly active. The noise disturbs one's sleep at first and sometimes, when an unusually heavy fall occurs, wakens one even after he has grown accustomed to the ordinary rumble. A sense of nervous relief is felt when camp is removed to a part of the fiord to which the iceberg roar and the breakers on 'the coast do not reach. This almost ceaseless activity of iceberg discharge testifies conclusively to the activity of the glacier behind. To supply so much falling ice (Pis. XIH, XLTV) there must be rapid movement up to the front. The broad stream of floating ice that stretches throughout Disenchantment Bay, and down Yakutat Bay to a distance fully 15 miles from the glacier front (PL L), offers further testimony in the same direction. And back of the ice cliff, where the surface from side to side is shattered by an impassable complex of yawning crevasses, sharp ice pinnacles, and seracs, one sees almost equally impressive evidence of rapid movement. The surface of Hubbard Glacier offers a strong contrast to that of the slowly-moving and stagnant ice masses, but resembles their condition during their brief periods of spasmodic advance. How fast the ice is moving is unknown, for no observations of rate have yet been made, but all facts indicate that, as glaciers go, it is a very rapidly moving ice stream. Concerning the reservoirs which supply this immense ice stream, and most of the tributaries which unite to form it, we have no further knowledge than that supplied by the Boundary Commission map.1 According to this map the sources of the Hubbard Glacier are far back among the lofty mountains of the St. Elias range, and probably in an ice-flooded area similar to that described by Russell as visible from the upper slopes of Mount St. Elias, No one has yet explored this region and the difficulties in the way of such exploration are great, though probably not impossible. We have been able to look far up the glacier, and as far as we could see, many miles from the coast, there is a 1 Atlas of Award, Akskan Boundary Tribunal, Sheet 28.